Routing cutter tools are employed in the machining of workpieces where it is required to remove from the workpiece substantial amounts of metal leaving precisely determined slots or recesses in the machined workpiece. A particular example of such routing operations is in the machining of aircraft structural components such as, for example, wing structures, wherein it is required to reduce to a maximum degree the weight of the structure whilst ensuring its mechanical strength. For this purpose the workpiece, usually formed of aluminum, is subjected to slotting and recessing, adjacent recesses in the workpiece being very often separated by extremely thin-walled portions. It will therefore be appreciated that the routing operation involves the removal of considerable quantities of metal and production efficiency requires a relatively high rate of such metal removal. At the same time, and in view of the fact that there remain in the machined component very thin separating walls, it is vital to ensure that the routing operation does not damage these thin-walled portions or induce undesirable stresses and strain therein.
Of its very nature, a routing operation involves an initial boring or drilling penetration of the workpiece by the cutting insert in the direction of the rotary axis of the cutting tool, and a subsequent milling operation involving a relative transverse displacement of the workpiece with respect to the rotary axis of the cutter tool. It has been proposed in this connection (GB 2 164 283) to provide a rotary routing cutter tool having a cutting insert wherein the rotary axis of the cutter tool is offset with respect to the cutting insert. Under these circumstances, and as is clearly explained and illustrated in this prior patent specification, the maximum depth to which the cutting insert can penetrate the workpiece in any single operation is limited. This limitation arises out of the fact that the insert does not have any cutting edge adjacent the rotary axis and there is therefore generated an upstanding core which limits the continued penetration of the cutting insert into the workpiece. In order to overcome this problem penetration and slotting takes place in a series of successive operations, in each of which the insert penetrates the workpiece by its predetermined maximum amount, then proceeds to reciprocate transversely from one end of the slot to the other, so as to remove the upstanding core. The routing operation therefore proceeds by way a series of successive ramps. It is therefore quite clear that this procedure, of necessity, reduces the rate of removal of the metal.
It is an object of the present invention to provide a new and improved cutting insert for a rotary routing cutter tool which facilitates an improved efficient rate of metal removal from a workpiece whilst minimizing the introduction of stresses into the workpiece during such removal.